This proposal focuses on neuroendocrine (NE) cells of the prostate and role they play in promoting androgen-independent growth of prostate tumors. Neuroendocrine (NE) cells are fully differentiated, postmitotic secretory cells that populate both normal and malignant prostate tissue. Morphologically, NE cells can be identified by their characteristic neuronal appearance, which includes the presence of long neuritic processes and dense secretory vesicles in the body. In prostate tumors the proliferative index of neoplastic epithelial cells surrounding the NE cells is frequently elevated, suggesting that the NE cells act in a paracrine fashion by secreting growth-inducing factors and contributing to the progression of the disease. Several of these factors have been identified and include serotonin, thyroid stimulating hormone (TSH), calcitonin, bombesin, and somatostatin. Increases in the number of NE cells also occur as part of tumor progression, presumably due to the influence of both genetic and epigenetic factors. The origin of these increased numbers in later stage prostatic carcinomas is uncertain, but several studies suggest that NE cells arise from within the tumor, either from a hyperplastic basal epithelial cell or from a transformed exocrine epithelial cell by de-differentiation or trans-differentiation, respectively. Bang et al. (9) have in fact shown that the prostate tumor cell lines, LNCaP and PC3M, can be induced to differentiate into post-mitotic NE-like cells upon addition of agents that increase intracellular cyclic AMP. These experiments provide evidence for the transdifferentiation model of NE cell derivation and suggest that physiological factors that elevate internal cAMP levels may play a role in the differentiation process. The goal of the studies described in this proposal is to identify physiological factors and critical signaling pathways that contribute to the differentiation of NE cells and to determine whether NE cells secrete paracrine signals which potentiate the growth of prostate carcinomas. To accomplish these aims, a panel of hormones and peptide factors that cause elevations in intracellular cAMP in LNCaP cells will be tested, and signaling pathways emanating from the most potent differentiating agents will be analyzed. In addition, a LacSwitch system will be generated that directs the regulated expression of a constitutively active form of the catalytic subunit of protein kinase A and used to differentiate prostate tumor cells lines to NE cells. Conditioned medium from these differentiated cells will then be tested for its ability to enhance proliferation of non-differentiated tumor cells. Finally, the signaling mechanisms regulating secretion will also be examined. The goals of the project are to elucidate signaling pathways that regulate differentiation and secretion of NE cells and to identify critcal components of these pathways that could serve as molecular targets for the development of novel therapies for late stage, androgen-independent prostate tumors.